When Is CVN Required Per AWS?

Date 03-29-2007 01:05

I will be working on two new WPS's soon, something we have not done for quite a few years. One is for GTAW of 17-4PH to itself and the other will be for GTAW of 4130 to itself. Applicable codes will be AWS D1.1 as well as Navy requirements for both.

AWS D1.1 (2006) seems to have a casual approach to CVN, relegating it to the customers responsibility: paragraph 4.1.1.3 stipulates, "when required by contract documents"; paragraph 4.7 states, "when CVN is specified"; paragraph 4.33 again states, "when specified in the contract documents".   The Navy requirement for Charpy testing seems to be a little more useful, it is based on if the material is over 1/2-inch thk AND if the specific material specification AND if the filler metal specification both have impact requirements.

In the case of my 17-4PH material spec (ASTM A564) it also has the blurb, "impact requirements shall apply when specified in the purchase order".   For my typical 4130 spec I find no mention of impact or CVN.
Now for the ER70S rods, the AWS A5.28 has all manner of mention for impact requirements (I don't know what filler we'll be using for the 17-4PH weldments yet) but it would seem to me the requirements in AWS A5.28 are there to qualify the filler to AWS A5.28, NOT for us to qualify a new WPS!!!

Advice I have received elsewhere is to "ask the customer", however, I have never seen an engineering drawing which identifies a weldment as requiring fracture tolerent welds! so I can't trust the customer to know if my WPS will require qualification w/CVN.

What are your recommendations on when must PQRT include CVN?

Thanks for letting me post my question, and thanks in advance for all advice.
Tom

By js55

Date 03-29-2007 13:38

I wouldn't say that AWS takes a casual approach to impacts. I would say AWS recognizes the bewildering diversity of applications that the code will be used for and therefore maintain minimalist safety philosophy that can be applied to as broad an industry as exists. It should be up to the design engineer to determine testing temps, minimum requirments, fracture concerns, service temps, ductile to brittle transitions, etc.
The code doesn't know if a structure is being built in Key West or Fargo. Whether its straddling the San Andreas or sittin on some massive unmovable bedrock.
I for one, do not know much about the toughness of Precip Hardening SS's. but it their DBTT properties are similar to austentics there may not even be a concern.
I'm sure those with some Precip Hardening experience can enlighten us some more.

By GRoberts (***)

Date 03-31-2007 07:25

For the 17-4PH, the matching filler metal is ER630. I don't believe that has impact requriements in the AWS A5.4 spec, but I don't have it handy to look at. It would be better to check it yourself to make sure. Not all 17-4PH welds need to be made with matching filler. If matching strength is not a concern, austenitic fillers can be used with good sucess. Also note that in section 1 of AWS D1.6, it specifies that stainless steel welding is to be in accordance with AWS D1.6, so D1.1 does not apply. The other thing you have to watch out for on 17-4PH is that you will notice that the base metal requiments for elongation are higher than for the filler metal. (At least it was for the base metal specs I have looked at.) I was using ASME IX at the time, and that did make it difficult since the bend test elongation requirements are based on the base metal's elongation requriemnts. So getting the filler metal to bend more than is required can be difficult.